(1) Field of the Invention
The present invention relates to the treatment of metallurgical slag and particularly to the fracturing of expanded slag by mechanical beating. More specifically, this invention is directed to beater apparatus which granulates blast furnace slag which has been expanded by treatment with water. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
U.S. Pat. No. 4,115,089 discloses a process of treating liquid blast furnace slag to produce a granulated product. In the patented process a flow of metallurgical slag is first treated with water to cause the expansion thereof and the expanded slag, which is still very hot, is subjected to a mechanical beating step to cause it to be broken into particulate form. The mechanical beating is performed by a rotating disintegration drum, indicated at 9 in the referenced patent, which is provided with outwardly extending beater bars. In the process, the expanded slag falls onto the disintegration drum, is broken up by the beater bars and subsequently ejected in a curved trajectory.
The apparatus of U.S. Pat. No. 4,115,089 may be used in the production of expanded slag, which is also known in the art as pumice slag, and also in the production of slag sand such as that which would be formed by means of a conventional granulating technique. The granulation of blast furnace slag is described in Luxembourg Pat. No. 77,160, dated Apr. 19, 1977, and its corresponding U.S. application Ser. No. 897,424. The production of slag sand is achieved by exercising control over the operating parameters of the apparatus and particularly the rotational speed of the disintegration drum and the quantity of water added to the molten slag. Thus, as drum speed is increased and also as the quantity of water added during the swelling or foaming phase of the process is increased, the ratio of the slag sand to pumice produced by the apparatus also increases.
The process briefly described above may be contrasted with the use of granulating pits as is also known in the prior art. A particularly important distinction between the use of a rotating disintegration drum to cause the break-up of the foamed slag, when compared to the use of a granulating pit, resides in the fact that the rotating drum technique offers a savings of up to 90% in water consumption. Accordingly, through the use of mechanical beating of the foamed slag, the apparatus required to separate the water from the slag sand or pumice slag, as well as the drying apparatus, will be less expensive to assemble and operate and thus more economical.
Experience has shown that the disintegration drums of apparatus of the types disclosed in referenced U.S. Pat. No. 4,115,089 have a comparatively limited service life. More particularly, these drums are subject to failure at the point of attachment of the beater bars thereto. While the drums themselves are water cooled, and the beater bars themselves may also be provided with passages through which a coolant is circulated, it has not previously been possible to achieve adequate cooling to insure that failure of the welds by which the beater bars are attached to the drum will not occur. Thus, the service life of disintegration drums has, in the prior art, averaged approximately 10,000 tons of slag.
It is also to be noted that, in interest of insuring adequate coolant circulation, it has been the practice in the prior art to discharge the coolant, which is typically water, through apertures in the disintegration drum whereby the coolant will be propelled from the vicinity of the drum along with the slag. This technique, however, results in the addition of the cooling water to that with which the slag has been treated to cause the foaming thereof and thus the total quantity of water which leaves the apparatus will be greater than necessary and/or the ability to exercise proper control over the process of preparation of the foamed slag is diminished.